/Engine/Source/Runtime/Slate/Public/Widgets/Layout/SBorder.h
A border is an widget that can be used to contain other widgets. It has a BorderImage property, which allows it to take on different appearances. Border also has aContent()slot as well as some parameters controlling the arrangement of said content.
class SBorder : public [SCompoundWidget](API\Runtime\SlateCore\Widgets\SCompoundWidget)